The atmosphere

The atmosphere of Uranus is composed of 83 per cent hydrogen, 15 per cent helium, 2 per cent methane, and tiny amounts of ethane and other hydrocarbon gases. The methane that is trapped high in the atmosphere absorbs red light from the visible spectrum, and this makes the planet appear blue-green in colour.

Voyager 2 data showed the atmosphere contains three distinct cloud layers. The top layer contains ammonia, the next layer ammonium hydrosulfide, and the third or lower layer contains water ice. These layers are found deep in Uranus's atmosphere, where temperatures and pressures are higher. The atmospheric pressure beneath the cloud layer is about 1.3 times that at the Earth's surface.

Like the other gas planets, Uranus has bands of clouds that blow around rapidly parallel to the equator. These bands are very faint and can only be

Figure 11.4 Uranus's atmosphere lacks detail in visible light but colour enhancement shows a dark polar region surrounded by a series of lighter concentric bands that may be smog or haze (Voyager 2). (Photo: NASA)

Figure 11.4 Uranus's atmosphere lacks detail in visible light but colour enhancement shows a dark polar region surrounded by a series of lighter concentric bands that may be smog or haze (Voyager 2). (Photo: NASA)

seen with image enhancement of the Voyager 2 photographs. Winds at mid-latitudes are propelled in the rotational direction of the planet. Winds at equatorial latitudes blow in the opposite direction.

Recent observations with the Hubble Space Telescope show larger and more pronounced streaks and some spots. The spots are probably violent swirling storms like a hurricane.